Optimism Upgrades to Multi-Chain Super Root for Cross-Chain Interoperability

Optimism has rolled out Upgrade 20 to its OP Stack network. This upgrade replaces the single-chain output root with a multi-chain super root. The new system is designed for cross-chain interoperability, allowing multiple chains to share data while keeping fault-proof dispute processes separate.

The multi-chain super root combines version byte, timestamp, and chain ID-output root pairs into a single hash, enabling it to represent the state of multiple chains at the same point in time. This upgrade is an incremental rollout aimed at reducing implementation risk.

Withdrawal proofs will continue to use output roots, ensuring existing withdrawal logic remains compatible with the new system. Node operators do not need to take action, but chain operators must update their configurations to support Upgrade 20.